The present invention relates to a rubber composition or, more particularly, to a rubber composition which is a composite consisting of a matrix phase of an unvulcanized rubbery elastomer such as fluorocarbon rubbers, EPDM rubbers and the like and a finely dispersed phase therein which is a cured silicone rubber comminuted so finely that particles of the silicone rubber are no longer visible. The rubber composition of the invention is capable of giving vulcanized rubber articles having excellent rubbery properties despite the outstanding inexpensiveness since scraps of cured silicone rubbers occurring in the molding and curing process of silicone rubber articles or reclaimed as a waste of silicone rubber articles after use can be used to provide the dispersed phase in the matrix of the unvulcanized rubbery matrix.
It is usual that scraps of vulcanized rubbers occurring in the molding and vulcanizing process as burrs or unacceptable products or obtained as a waste material after prolonged use of vulcanized rubber articles are not always discarded as such but are recycled and re-used as a reclaimed rubber after refining by washing, pulverization, desulfurization and the like into a rubber powder having a particle size of 30 to 80 mesh, which can be compounded in a considerably large amount with an unvulcanized rubber stock under a shearing force to be dispersed in the matrix of the unvulcanized rubber to such an extent that the particles of the reclaimed rubber are no longer visible to the naked eyes. Such a composite rubber stock containing a powder of the reclaimed rubber can be again molded and vulcanized into vulcanized rubber articles having rubbery properties comparable to those prepared from a fresh rubber alone so that economical advantages are obtained owing to the inexpensiveness of the reclaimed rubber as compared with a fresh rubber.
As to silicone rubbers as a class of synthetic rubbers, the production and consumption of silicone rubber articles are rapidly growing more and more in a variety of application fields by virtue of the excellent properties thereof as compared with other organic synthetic rubbers such as heat and cold resistance, weatherability, electric insulation, etc., such that the amount of scraps of cured silicone rubbers, occurring as burrs and unacceptable products in the molding process of silicone rubber articles is also rapidly increasing and as a waste of used-up silicone rubber articles. Nevertheless, no efficient way has yet been established for recycling and re-using scraps of cured silicone rubber articles. Scraps of cured silicone rubber articles can of course be converted into a fine powder in a way similar to that for organic rubbers mentioned above but, when such a powder of reclaimed silicone rubber scraps is blended with a fresh uncured silicone rubber and the composite silicone rubber stock is molded and cured into cured silicone rubber articles, the reclaimed silicone rubber can never be fully comminuted to such a fineness that the particles thereof are no longer visible to the naked eyes. Instead the particles remain as a heterogeneous phase in the matrix of the fresh silicone rubber and eventually the particles of the reclaimed silicone rubber fall out of the cured silicone rubber body. Accordingly, the result is that such a cured silicone rubber article prepared by blending a powder of reclaimed silicone rubber scraps is very inferior in mechanical strengths as well as in the permanent compression set and heat resistance. Thus, no practically applicable way is known for the efficient utilization of scraps of cured silicone rubbers so that the only way to dispose scraps of cured silicone rubbers is just to discard them as a waste material of nuisance. Therefore, it is eagerly desired to develop an efficient way to effectively utilize such cured silicone rubber scraps.